376 GERMINAL ORGANIZATION INDUCTION PHENOMENA 4 



method called affixation was also used (Hama, 1949). With either method, a 

 close adherence between inductor and reactor is obtained. The purpose of the 

 experiment can be understood (Okada and Hama, 1945b) by considering 

 Fig. 46. 



At the appearance of the blastopore, the material of the lip {a) is shown by combined 

 staining (coarse stippling, Nile blue; fine stippling, neutral red) to contain material which 

 at the large yolk plug stage {c) will form the anterior half of the archenteric roof (c, coarse 

 and fine stippling). This territory is already known, from Gallera's experiments (p. 375), 

 to contain endoblast anteriorly, endo-mesoblast laterally, prechordal plate in the inter- 

 mediate median part. This area corresponds roughly to Spemann's head organizer. If the 

 lip is stained a few hours later when the blastoporal groove has deepened {b), the material 

 there will be devoted to the hind part of the roof (coarse stippled in c) and is equivalent 

 to Spemann's trunk organizer. Once this topography had been established, 27 transplan- 

 tations of the stained fragment shown in (a) uniformly resulted "not only in the absence 

 of a single instance in which the induced structure could be identified unmistakably as 

 a head, but also in the occurrence of many instances in which a trunk or a tail was induced" 

 (their p. 507). Indeed, this result was the same as when the stained material of {c) was trans- 

 planted. Then, at this second stage and at a somewhat later one, the roof of the blastoporal 

 groove was dissected, and its anterior and posterior parts were used for the same kind of 

 grafting. The percentage and size of inductions was reduced, which is in agreement with 

 Gallera's observations. "Grafts of anterior regions stimulated the formation of head 

 organs regardless of their position in the host . . . while grafts of posterior regions were 

 always limited to the induction of a tail" (also their p. 507). Further, "it can be said with 

 certainty that neither a tail was formed by grafts of the anterior half nor a head by grafts 

 of the posterior half" {ibid). This clear-cut result hinted at the possibility of a diflference 

 existing between the performances of the same material taken before and after invagina- 

 tion. Consequently, an accurate comparison was done between the inductive ability of 

 grafts formed respectively of corresponding invaginated and uninvaginated material 

 between stages {a) and (c). "The results were very clear: as often as the uninvaginated 

 portion of the dorsal lip of each of the gastrula stages affected induction, regardless of the 

 site of the transplant, the induced body was without exception either trunk or tail, or at 

 times both ... In contrast to this, the portion which had already invaginated to form the 

 dorsal wall of the archenteron always stimulated the development of a head" (p. 509). It is 

 remarkable that this was already true for the narrow invaginated portion of the shallow 

 blastopore at stage {a) as shown in Fig. 47, a. Naturally, when invaginated material is 

 obtained from stage (c), just under the lip, it induces only structures of trunk or tail type. 

 The acquisition, as the result of invagination, of the new property of inducing the acrenceph- 

 alon only concerns material which travels over the blastoporal lip before stage (c). The 

 change is also revealed in sections by diflferential staining with thionin: the uninvaginated 

 part stains blue, the invaginated part red (Hama in Okada and Hama, 1948, their p. 34). 

 Finally, the authors examined whether other conditions would have the same effect. They 

 found that culturing the uninvaginated fragment of stage {a) in vitro for more than 20 h. 

 incited the power of inducing head organs. The same result can be obtained by cultivation 

 in the blastocoele of a blastula, although only after a longer delay (24 to 26 h.). Accordingly, 

 the authors exclude the idea that the kinematic activities could be responsible for the 

 acquisition of the new inducing properties ; an intrinsic maturation process would be the 

 real cause, the two phenomena being parallel in time. This is an opinion to which we shall 

 have to return. 



Extending their enquiry to the whole dorso-marginal region, Okada and Takaya 

 found that the same modification could be obtained, by in vitro cultivation, in a 

 larger territory than the young blastoporal lip, though only in its immediate 

 vicinity. This means that this territory is predisposed to exhibit this important 

 property. 



